Proteins, which are compounds made of nitrogen-rich amino acids, create waste products in the body of animals that must be eliminated. which toxic compound is the primary concern of animal waste systems?
a. ammonium
b. nitrogen
c. urea
d. ammonia

bacterium is not correct

i think it is d. objects resist changes in their state of motion.

the earth is thought to have been formed about 4.6 billion years ago by collisions from a cloud of hydrogen, helium, rock, ice and other materials. these were pulled together by gravity to form objects in and around earth like- asteroids and small early planets called planetesimals.

so, the best possible answer to this question will be option d- to harden materials to form different parts of earth’s layers